Quicklime

Quicklime, CaO (calcium oxide), also called hical lime, is produced by the calcination of limestone, CaCO₃ (calcium carbonate). Crushed limestone is heated to around 1,100 degrees Celsius in kilns to produce quicklime. The heating of limestone releases carbon dioxide, leaving calcium oxide (CaCO₃ produces CaO + CO₂). 

Quicklime has a wide range of uses, including in the production of iron and steel, paper and pulp production, treatment of water and flue gases and in the mining industry.